[ios, macos] Add mgl_coalesce conventional custom function support.

2 files changed, 25 insertions, 7 deletions

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 2af636516e..4f5739aaa1 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -409,6 +409,12 @@
     return [self valueForKeyPath:@"mgl_jsonExpressionObject"];
 }
 
+- (id)mgl_coalesce {
+    [NSException raise:NSInvalidArgumentException
+                      format:@"Coalesce expressions lack underlying Objective-C implementations."];
+    return nil;
+}
+
 @end
 
 @implementation NSDictionary (MGLExpressionAdditions)
@@ -861,14 +867,10 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             } else if ([function isEqualToString:@"MGL_MATCH"] ||
                        [function isEqualToString:@"mgl_match:"]) {
                 return self.mgl_jsonMatchExpressionObject;
-            } else if ([function isEqualToString:@"mgl_coalesce:"]) {
-                NSMutableArray *expressionObject = [NSMutableArray arrayWithObjects:@"coalesce", nil];
+            } else if ([function isEqualToString:@"mgl_coalesce:"] ||
+                       [function isEqualToString:@"mgl_coalesce"]) {
                 
-                for (NSExpression *expression in self.arguments.firstObject.constantValue) {
-                    [expressionObject addObject:[expression mgl_jsonExpressionObject]];
-                }
-                
-                return expressionObject;
+                return self.mgl_jsonCoalesceExpressionObject;
             } else if ([function isEqualToString:@"castObject:toType:"]) {
                 id object = self.arguments.firstObject.mgl_jsonExpressionObject;
                 NSString *type = self.arguments[1].mgl_jsonExpressionObject;
@@ -1053,4 +1055,15 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
     return expressionObject;
 }
 
+- (id)mgl_jsonCoalesceExpressionObject {
+    BOOL isAftermarketFunction = [self.function isEqualToString:@"mgl_coalesce:"];
+    NSMutableArray *expressionObject = [NSMutableArray arrayWithObjects:@"coalesce", nil];
+    
+    for (NSExpression *expression in  (isAftermarketFunction ? self.arguments.firstObject : self.operand).constantValue) {
+        [expressionObject addObject:[expression mgl_jsonExpressionObject]];
+    }
+    
+    return expressionObject;
+}
+
 @end
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 17c48af226..20209f305e 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -658,8 +658,13 @@ using namespace std::string_literals;
                                       [NSExpression expressionForKeyPath:@"y"],
                                       [NSExpression expressionForKeyPath:@"z"],
                                       [NSExpression expressionForConstantValue:@0]]];
+        NSExpression *compatibilityExpression = [NSExpression expressionWithFormat:@"FUNCTION(%@, 'mgl_coalesce')", @[[NSExpression expressionForKeyPath:@"x"],
+                                                                                                                      [NSExpression expressionForKeyPath:@"y"],
+                                                                                                                      [NSExpression expressionForKeyPath:@"z"],
+                                                                                                                      [NSExpression expressionForConstantValue:@0]]];
         NSArray *jsonExpression = @[@"coalesce", @[@"get", @"x"], @[@"get", @"y"], @[@"get", @"z"], @0];
         XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects(compatibilityExpression.mgl_jsonExpressionObject, jsonExpression);
         XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
     }